Making Triplets

Soon after the closest star to the Sun was discovered, in 1915, astronomers began suspecting that it was gravitationally bound to two other stars. But it’s been hard to confirm that suspicion.
The stars are the binary system Alpha Centauri A and B, and Proxima Centauri. A and B look like a single pinpoint — one of the brightest in the night sky. Proxima is a cosmic ember so faint that you need a good telescope to see it.
Proxima is just four and a quarter light-years from Earth. The other two are a bit farther. But all three stars move through space in the same way.
Proxima is sometimes called Alpha Centauri C, indicating that it’s the third member of the system. Because of the distance between it and the stars A and B, though, that designation has been shaky. We hadn’t seen enough of Proxima’s possible orbit to confirm its membership.
Some recent studies have solidified that membership, though. One, released last summer, carefully measured the details of the system. Among other things